Thursday, 15 March 2012

How to create and test WCF Web Service

Let's say we want to create Calculator service which exposes methods that return results of addition, subtraction, multiplication and division applied on provided operands. These operations always take two operands so we can group them in a class Operands.

Now we can define interface of such web service:

Once we have have a clear image of exposed web methods and data types we can start implementing web service. In Visual Studio (I am using VS2010), go to File -> New -> Project... and create Visual C# WCF Service Library project named CalculatorServiceLibrary. Make sure you are using the latest .NET Framework (e.g. version 4.0). Visual Studio creates project skeleton with following files:

IService1.cs (service interface definition file):

Service1.cs (service interface implementation file):

App.config:

These auto-generated files give us a hint how to organize the code and we need to modify them, inserting specifics of our service.

WCF is a framework for building Service Oriented Architecture (SOA) applications. SOA requires defining protocols on messages and data exchanged between service and client. They are known as Service and Data Contracts and are supported by WCF.

Web Service interface definition file contains these contracts.

Service Contract defines operations exposed by the service. [ServiceContract] attribute applied to an interface (or class) tells it represents a service contract. Interface or class methods that are to be exposed as service operations are marked with [OperationContract] attribute.

Data exchanged between client and service (service operations arguments and return values) is described through Data Contract. All data is embedded into SOAP messages which are XML-based so data types must be serializable. All primitive .NET types are serializable by default and have default data contracts. But custom types that are part of data contract must be marked with [DataContract] attribute which defines them to be serializable. Type members that are part of data contract must be marked with [DataMember] attribute.

In our case, custom data type is class Operands and we need to mark it as [DataContract]. We can rename IService1.cs and Service1.cs to ICalculatorService.cs and CalculatorService.cs. After modifying the interface, its implementation class and data type, these files look like this:

ICalculatorService.cs:

CalculatorService.cs:

[ServiceBehavior] attribute controls various aspects of service object behaviour. In our case we specified that there will be only a single instance of the service object created on the server and that only a single thread at a time will be allowed to process method calls. This means that one client would need to wait for another's client web method call to complete. In our simple example this is acceptable but if amount of processing within web methods was higher, a different behaviour model would need to be applied.

Before compiling our project we yet need to modify application configuration file (App.config). Let us rename service to "CalculatorServiceLibrary.CalculatorService" and name behavior as "MetadataEnabled". In order to enable generating WSDL we need to add reference to this behavior as a service attribute: behaviorConfiguration="MetadataEnabled" and add httpGetUrl="mex" to behavior's serviceMetadata element. URL of the WSDL can now be made by appending "/mex" to the base address.

By default, service endpoint binding is set to wsHttpBinding which encrypts messages. For our convenience, as we will be using HTTP sniffer later, let us apply basicHttpBinding, which does not apply encryption. This way we will be able to see unencrypted data in HTTP messages exchanged between server and client.

Yet another thing set by default is to be changed: service endpoint contract - let us rename it to "CalculatorServiceLibrary.ICalculatorService".

App.config will have the final look:

We are now ready to build this project. If we build it in Debug mode, project's Debug directory will contain CalculatorServiceLibrary.dll and CalculatorServiceLibrary.dll.config. This config file is a pure copy of App.config visible and editable from Visual Studio.

We can test our web service from Visual Studio if we run the project (press F5 key). This will start WCF Service Host and WCF Test Client tools. Service will automatically be deployed on the host and the client will use published metadata information in order to build a list of web methods (matadata is fetched from endpoint that implements IMetadataExchange contract). We can type in arguments and invoke web methods in the Test Client.

WCF Service Host:

WCF Test Client:

In order to see generated WSDL we can copy metadata address (WSDL URL; in our example: http://localhost:8732/Design_Time_Addresses/CalculatorServiceLibrary/Service1/mex) from Web Service Host and paste it into a web browser:

Generated WSDL for this service is:

We can run WCF Service Host out of Visual Studio, from command prompt:

If this instance of the host cannot create endpoint (cannot listen) on the port 8732 (because previous instance run from Visual Studio has locked it), enter some other port number in baseAddress in App.config (e.g. 8733).